My tomato plants (Porter's purchased from Dillard Feed, Weatherford)look wonderful, bloom appropriately but the tomatoes are very meaty and sour when cut open, uneatable. What causes this? I've never had a problem with vegetable taste before. The only thing I did differently this year is broadcast kelp over the area where the tomatoes are. Does kelp have a lot of salt in it? Thank You Very Much.

what variety?

As noted above--Porter indeterminate and I think this is an heirloom one, but I could be wrong about that.